physicochemical treatment processes

Physicochemical Treatment Processes
Physicochemical
Treatment Processes
Edited by
Lawrence K. Wang, PhD, PE, DEE
Zorex Corporation, Newtonville, NY
Lenox Institute of Water Technology, Lenox, MA
Krofta Engineering Corporation, Lenox, MA
Yung-Tse Hung, PhD, PE, DEE
Department of Civil and Environmental Engineering
Cleveland State University, Cleveland, OH
Nazih K. Shammas, PhD
Lenox Institute of Water Technology, Lenox, MA
VOLUME 3
HANDBOOK OF ENVIRONMENTAL ENGINEERING
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eISBN 1-59259-820-x
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Library of Congress Cataloging-in-Publication Data
Physicochemical treatment processes / edited by Lawrence K. Wang, Yung-Tse Hung, Nazih K. Shammas.
p. cm. — (Handbook of environmental engineering)
Includes bibliographical references and index.
ISBN 1-58829-165-0 (v. 3 : alk. paper)
1. Water—Purification. 2. Sewerage—Purification. I. Wang, Lawrence K. II. Hung, Yung-Tse. III.
Shammas, Nazih K. IV Series: Handbook of environmental engineering (2004) ; v. 3.
TD170 .H37 2004 vol. 3
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Preface
v
The past 30 years have seen the emergence of a growing desire worldwide to take
positive actions to restore and protect the environment from the degrading effects of all
forms of pollution: air, noise, solid waste, and water. Because pollution is a direct or
indirect consequence of waste, the seemingly idealistic demand for “zero discharge”
can be construed as an unrealistic demand for zero waste. However, as long as waste
exists, we can only attempt to abate the subsequent pollution by converting it to a less
noxious form. Three major questions usually arise when a particular type of pollution
has been identified: (1) How serious is the pollution? (2) Is the technology to abate it

available? and (3) Do the costs of abatement justify the degree of abatement achieved?
The principal intention of the Handbook of Environmental Engineering series is to
help readers formulate answers to the last two questions.
The traditional approach of applying tried-and-true solutions to specific pollution prob-
lems has been a major contributing factor to the success of environmental engineering, and
has accounted in large measure for the establishment of a “methodology of pollution con-
trol.” However, realization of the ever-increasing complexity and interrelated nature of
current environmental problems makes it imperative that intelligent planning of pollution
abatement systems be undertaken. Prerequisite to such planning is an understanding of the
performance, potential, and limitations of the various methods of pollution abatement avail-
able for environmental engineering. In this series of handbooks, we will review at a tutorial
level a broad spectrum of engineering systems (processes, operations, and methods) cur-
rently being utilized, or of potential utility, for pollution abatement. We believe that the
unified interdisciplinary approach in these handbooks is a logical step in the evolution of
environmental engineering.
The treatment of the various engineering systems presented in Physicochemical
Treatment Process shows how an engineering formulation of the subject flows natu-
rally from the fundamental principles and theories of chemistry, physics, and math-
ematics. This emphasis on fundamental science recognizes that engineering practice
has in recent years become more firmly based on scientific principles rather than its
earlier dependency on empirical accumulation of facts. It is not intended, though, to
neglect empiricism when such data lead quickly to the most economic design; certain
engineering systems are not readily amenable to fundamental scientific analysis, and in
these instances we have resorted to less science in favor of more art and empiricism.
Because an environmental engineer must understand science within the context of appli-
cation, we first present the development of the scientific basis of a particular subject, fol-
lowed by exposition of the pertinent design concepts and operations, and detailed
explanations of their applications to environmental quality control or improvement.
Throughout this series, methods of practical design calculation are illustrated by numerical
examples. These examples clearly demonstrate how organized, analytical reasoning leads

to the most direct and clear solutions. Wherever possible, pertinent cost data have been
provided.
Our treatment of pollution-abatement engineering is offered in the belief that the
trained engineer should more firmly understand fundamental principles, be more aware
of the similarities and/or differences among many of the engineering systems, and ex-
hibit greater flexibility and originality in the definition and innovative solution of envi-
ronmental pollution problems. In short, environmental engineers should by conviction
and practice be more readily adaptable to change and progress.
Coverage of the unusually broad field of environmental engineering has demanded
an expertise that could only be provided through multiple authorships. Each author (or
group of authors) was permitted to employ, within reasonable limits, the customary
personal style in organizing and presenting a particular subject area, and, consequently,
it has been difficult to treat all subject material in a homogeneous manner. Moreover,
owing to limitations of space, some of the authors’ favored topics could not be treated
in great detail, and many less important topics had to be merely mentioned or com-
mented on briefly. All of the authors have provided an excellent list of references at the
end of each chapter for the benefit of the interested reader. Because each of the chap-
ters is meant to be self-contained, some mild repetition among the various texts was
unavoidable. In each case, all errors of omission or repetition are the responsibility of
the editors and not the individual authors. With the current trend toward metrication,
the question of using a consistent system of units has been a problem. Wherever pos-
sible the authors have used the British system along with the metric equivalent or vice
versa. The authors sincerely hope that this doubled system of unit notation will prove
helpful rather than disruptive to the readers.
The goals of the Handbook of Environmental Engineering series are: (1) to cover the
entire range of environmental fields, including air and noise pollution control, solid waste
processing and resource recovery, biological treatment processes, water resources, natu-
ral control processes, radioactive waste disposal, thermal pollution control, and physico-
chemical treatment processes; and (2) to employ a multithematic approach to
environmental pollution control because air, water, land, and energy are all interre-

lated. The organization of the series is mainly based on the three basic forms in which
pollutants and waste are manifested: gas, solid, and liquid. In addition, noise pollution
control is included in one of the handbooks in the series.
This volume, Physicochemical Treatment Processes, has been designed to serve as a
basic physicochemical treatment text as well as a comprehensive reference book. We
hope and expect it will prove to be of high value to advanced undergraduate or gradu-
ate students, to designers of water and wastewater treatment systems, and to research
workers. The editors welcome comments from readers in all these categories. It is our
hope that this book will not only provide information on the physical, chemical, and
mechanical treatment technologies, but will also serve as a basis for advanced study or
specialized investigation of the theory and practice of the individual physicochemical
systems covered.
The editors are pleased to acknowledge the encouragement and support received
from their colleagues and the publisher during the conceptual stages of this endeavor.
We wish to thank the contributing authors for their time and effort, and for having
vi Preface
patiently borne our reviews and numerous queries and comments. We are very grateful
to our respective families for their patience and understanding during some rather try-
ing times.
Lawrence K. Wang
Yung-Tse Hung
Nazih K. Shammas
Preface vii
ix
Contents
Preface v
Contributors xix
1 Screening and Comminution
Frank J. DeLuise, Lawrence K. Wang, Shoou-Yuh Chang,
and Yung-Tse Hung 1

1. Function of Screens and Comminutors 1
2. Types of Screens 2
2.1. Coarse Screens 2
2.2. Fine Screens 2
3. Physical Characteristics and Hydraulic Considerations of Screens 3
4. Cleaning Methods for Screens 5
5. Quality and Disposal for Screens 6
6. Comminutors 7
7. Engineering Specifications and Experience 8
7.1. Professional Association Specifications 8
7.2. Engineering Experience 11
8. Engineering Design 12
8.1. Summary of Screening Design Considerations 12
8.2. Summary of Comminution Design Considerations 14
9. Design Examples 15
9.1. Example 1: Bar Screen Design 15
9.2. Example 2: Bar Screen Head Loss 16
9.3. Example 3: Plugged Bar Screen Head Loss 17
9.4. Example 4: Screen System Design 17
Nomenclature 18
References 18
2 Flow Equalization and Neutralization
Ramesh K. Goel, Joseph R. V. Flora, and J. Paul Chen 21
1. Introduction 21
2. Flow Equalization 21
2.1. Flow Equalization Basin Calculations 23
2.2. Mixing and Aeration Requirements 25
2.3. Mixer Unit 26
3. Neutralization 28
3.1. pH 28

3.2. Acidity and Alkalinity 29
3.3. Buffer Capacity 30
3.4. Hardness 31
4. Neutralization Practices 32
4.1. Neutralization of Acidity 32
4.2. Neutralization of Alkalinity 33
4.3. Common Neutralization Treatments 34
5. pH Neutralization Practices 36
5.1. Passive Neutralization 36
5.2. In-Plant Neutralization 36
5.3. Influent pH Neutralization 36
5.4. In-Process Neutralization 37
5.5. Effluent Neutralization 38
5.6. Chemicals for Neutralization 38
5.7. Encapsulated Phosphate Buffers for In Situ Bioremediation 39
6. Design of a Neutralization System 39
7. Design Examples 40
Nomenclature 43
References 44
3 Mixing
J. Paul Chen, Frederick B. Higgins, Shoou-Yuh Chang,
and Yung-Tse Hung 47
1. Introduction 47
2. Basic Concepts 48
2.1. Criteria for Mixing 50
2.2. Mixing Efficiency 52
2.3. Fluid Shear 54
3. Mixing Processes and Equipment 55
3.1. Mixing in Turbulent Fields 55
3.2. Mechanical Mixing Equipment 58

3.3. Impeller Discharge 69
3.4. Motionless Mixers 71
3.5. Mixing in Batch and Continuous Flow Systems 73
3.6. Suspension of Solids 77
3.7. Static Mixer 84
4. Design of Facilities 86
4.1. Pipes, Ducts, and Channels 86
4.2. Self-Induced and Baffled Basins 89
4.3. Mechanically Mixed Systems 90
Nomenclature 99
References 100
4 Coagulation and Flocculation
Nazih K. Shammas 103
1. Introduction 103
2. Applications of Coagulation 104
2.1. Water Treatment 104
2.2. Municipal Wastewater Treatment 104
2.3. Industrial Waste Treatment 104
2.4. Combined Sewer Overflow 104
2.5. Factors to be Considered in Process Selection 105
3. Properties of Colloidal Systems 105
3.1. Electrokinetic Properties 105
3.2. Hydration 106
3.3. Brownian Movement 106
3.4. Tyndall Effect 106
3.5. Filterability 107
4. Colloidal Structure and Stability 107
5. Destabilization of Colloids 109
5.1. Double-Layer Compression 110
5.2. Adsorption and Charge Neutralization 110

5.3. Entrapment of Particles in Precipitate 111
5.4. Adsorption and Bridging between Particles 111
6. Influencing Factors 112
6.1. Colloid Concentration 112
6.2. Coagulant Dosage 112
6.3. Zeta Potential 112
6.4. Affinity of Colloids for Water 113
6.5. pH Value 113
6.6. Anions in Solution 114
x Contents
6.7. Cations in Solution 114
6.8. Temperature 114
7. Coagulants 114
7.1. Aluminum Salts 115
7.2. Iron Salts 116
7.3. Sodium Aluminate 116
7.4. Polymeric Inorganic Salts 117
7.5. Organic Polymers 117
7.6. Coagulation Aids 118
8. Coagulation Control 118
8.1. Jar Test 119
8.2. Zetameter 120
8.3. Streaming Current Detector 121
9. Chemical Feeding 121
10. Mixing 122
11. Rapid Mix 124
12. Flocculation 125
13. Design Examples 127
Nomenclature 137
References 138

5 Chemical Precipitation
Lawrence K. Wang, David A. Vaccari, Yan Li, and Nazih K. Shammas 141
1. Introduction 141
2. Process Description 142
3. Process Types 142
3.1. Hydroxide Precipitation 142
3.2. Sulfide Precipitation 144
3.3. Cyanide Precipitation 145
3.4. Carbonate Precipitation 145
3.5. Coprecipitation 146
3.6. Technology Status 146
4. Chemical Precipitation Principles 146
4.1. Reaction Equilibria 146
4.2. Solubility Equilibria 147
4.3. Ionic Strength and Activity 148
4.4. Ionic Strength Example 149
4.5. Common Ion Effect 150
4.6. Common Ion Effect Example 150
4.7. Soluble Complex Formation 151
4.8. pH Effect 152
4.9. Solubility Diagrams 152
5. Chemical Precipitation Kinetics 152
5.1. Nucleation 153
5.2. Crystal Growth 153
5.3. Aging 154
5.4. Adsorption and Coprecipitation 154
6. Design Considerations 155
6.1. General 155
6.2. Chemical Handling 155
6.3. Mixing, Flocculation, and Contact Equipment 156

6.4. Solids Separation 157
6.5. Design Criteria Summary 157
7. Process Applications 158
7.1. Hydroxide Precipitation 158
7.2. Carbonate Precipitation 159
7.3. Sulfide Precipitation 160
7.4. Cyanide Precipitation 161
7.5. Magnesium Oxide Precipitation 162
Contents xi
7.6. Chemical Oxidation–Reduction Precipitation 162
7.7. Lime/Soda-Ash Softening 162
7.8. Phosphorus Precipitation 162
7.9. Other Chemical Precipitation Processes 163
8. Process Evaluation 163
8.1. Advantages and Limitations 163
8.2. Reliability 164
8.3. Chemicals Required 165
8.4. Residuals Generated 165
8.5. Process Performance 165
9. Application Examples 165
Nomenclature 169
References 170
Appendices 174
6 Recarbonation and Softening
Lawrence K. Wang, Jy S. Wu, Nazih K. Shammas,
and David A. Vaccari 199
1. Introduction 199
2. Process Description 199
3. Softening and Recarbonation Process Chemistry 201
4. Lime/Soda Ash Softening Process 203

5. Water Stabilization 205
6. Other Related Process Applications 206
6.1. Chemical Coagulation Using Magnesium Carbonate as a Coagulant 206
6.2. Recovery of Magnesium as Magnesium Carbonate 207
6.3. Recovery of Calcium Carbonate as Lime 207
6.4. Recarbonation of Chemically Treated Wastewaters 208
7. Process Design 208
7.1. Sources of Carbon Dioxide 208
7.2. Distribution Systems 210
7.3. Carbon Dioxide Quantities 212
7.4. Step-by-Step Design Approach 212
8. Design and Application Examples 215
Nomenclature 226
Acknowledgments 227
References 227
7 Chemical Oxidation
Nazih K. Shammas, John Y. Yang, Pao-Chiang Yuan,
and Yung-Tse Hung 229
1. Introduction 229
1.1. Dissolved Oxygen and Concept of Oxidation 230
1.2. The Definition of Oxidation State 231
2. Theory and Principles 233
2.1. Stoichiometry of Oxidation–Reduction Processes 234
2.2. Thermodynamics of Chemical Oxidation 236
2.3. Kinetic Aspects of Chemical Oxidation 240
3. Oxygenated Reagent Systems 243
3.1. Aeration in Water Purification and Waste Treatment 243
3.2. Hydrogen Peroxide and Peroxygen Reagents 246
3.3. High-Temperature Wet Oxidation 248
4. Transition-Metal Ion Oxidation Systems 256

4.1. Chromic Acid Oxidation 256
4.2. Permanganate Oxidation 258
5. Recent Developments in Chemical Oxidation 261
5.1. Ozone (O
3
) Processes 261
5.2. Ultraviolet (UV) Processes 262
5.3. Wet Oxidation 263
xii Contents
5.4. Supercritical Water Oxidation 264
5.5. Biological Oxidation 264
6. Examples 264
Nomenclature 268
References 269
8 Halogenation and Disinfection
Lawrence K. Wang, Pao-Chiang Yuan, and Yung-Tse Hung 271
1. Introduction 271
2. Chemistry of Halogenation 274
2.1. Chlorine Hydrolysis 274
2.2. Chlorine Dissociation 275
2.3. Chlorine Reactions with Nitrogenous Matter 275
2.4. Chlorine Reactions with Other Inorganics 279
2.5. Chlorine Dioxide (ClO
2
) Applications 281
2.6. Chlorine Dioxide Generation 281
2.7. Chlorine Dioxide Reaction with Nitrogenous Matter 282
2.8. Chlorine Dioxide Reactions with Phenolic Compounds and Other Substances 283
2.9. Bromine Hydrolysis 283
2.10. Bromine Dissociation 283

2.11. Bromine Reactions with Nitrogenous Matter 284
2.12. Iodine Hydrolysis 284
2.13. Iodine Dissociation 284
2.14. Iodine Reactions with Nitrogenous Matter 285
3. Disinfection with Halogens 285
3.1. Modes and Rate of Killing in Disinfection Process 285
3.2. Disinfection Conditions 286
3.3. Disinfection Control with Biological Tests 287
3.4. Disinfectant Concentration 288
4. Chlorine and Chlorination 288
4.1. Chlorine Compounds and Elemental Chlorine 289
4.2. Chlorine Feeders 290
4.3. Chlorine Handling Equipment 291
4.4. Measurement of Chlorine Residuals 291
4.5. Chlorine Dosages 292
4.6. Chlorination By-Products 293
5. Chlorine Dioxide Disinfection 294
6. Bromine and Bromination 294
7. Iodine and Iodination 295
8. Ozone and Ozonation 295
9. Cost Data 295
10. Recent Developments in Halogenation Technology 296
10.1. Recent Environmental Concerns and Regulations 296
10.2. Chlorine Dioxide 297
10.3. Chloramines 298
10.4. Coagulant 298
10.5. Ozone 299
10.6. Organic Disinfectants 299
10.7. Ultraviolet (UV) 300
11. Disinfection System Design 300

11.1. Design Considerations Summary 300
11.2. Wastewater Disinfection 301
11.3. Potable Water Disinfection 303
12. Design and Application Examples 305
12.1. Example 1 (Wastewater Disinfection) 305
12.2. Example 2 (Potable Water Disinfection) 308
12.3. Example 3 (Glossary of Halogenation, Chlorination, Oxidation, and Disinfection) 308
Nomenclature 311
References 311
Contents xiii
9 Ozonation
Nazih K. Shammas and Lawrence K. Wang 315
1. Introduction 315
1.1. General 315
1.2. Alternative Disinfectants 316
2. Properties and Chemistry of Ozone 316
2.1. General 316
2.2. Physical Properties 316
2.3. Chemical Properties 317
2.4. Advantages and Disadvantages 319
3. Applications of Ozone 319
3.1. Disinfection Against Pathogens 319
3.2. Zebra Mussel Abatement 320
3.3. Iron and Manganese Removal 320
3.4. Color Removal 320
3.5. Control of Taste and Odor 321
3.6. Elimination of Organic Chemicals 321
3.7. Control of Algae 321
3.8. Aid in Coagulation and Destabilization of Turbidity 321
4. Process and Design Considerations 321

4.1. Oxygen and Ozone 321
4.2. Disinfection of Water by Ozone 322
4.3. Disinfection of Wastewater by Ozone 324
4.4. Disinfection By-Products 333
4.5. Oxygenation by Ozone 334
4.6. Advanced Oxidation Processes 337
5. Ozonation System 340
5.1. Air Preparation 341
5.2. Electrical Power Supply 344
5.3. Ozone Generation 344
5.4. Ozone Contacting 345
5.5. Destruction of Ozone Contactor Exhaust Gas 348
5.6. Monitors and Controllers 349
6. Costs of Ozonation Systems 349
6.1. Equipment Costs 349
6.2. Installation Costs 352
6.3. Housing Costs 353
6.4. Operating and Maintenance Costs 353
7. Safety 353
Nomenclature 354
References 355
10 Electrolysis
J. Paul Chen, Shoou-Yuh Chang, and Yung-Tse Hung 359
1. Introduction 359
2. Mechanisms of Electrolysis 362
3. Organic and Suspended Solids Removal 363
3.1. Organic and Suspended Solids Removal by Regular Electrolysis 363
3.2. Organic and Suspended Solids Removal by Electrocoagulation 364
4. Disinfection 366
5. Phosphate Removal 368

6. Ammonium Removal 369
7. Cyanide Destruction 369
8. Metal Removal 370
9. Remediation of Nitroaromatic Explosives-Contaminated Groundwater 372
10. Electrolysis-Stimulated Biological Treatment 374
10.1. Nitrogen Removal 375
10.2. Electrolytic Oxygen Generation 374
References 376
xiv Contents
11 Sedimentation
Nazih K. Shammas, Inder Jit Kumar, Shoou-Yuh Chang,
and Yung-Tse Hung 379
1. Introduction 379
1.1. Historical 379
1.2. Definition and Objective of Sedimentation 380
1.3. Significance of Sedimentation in Water and Wastewater Treatment 380
2. Types of Clarification 380
3. Theory of Sedimentation 381
3.1. Class 1 Clarification 382
3.2. Class 2 Clarification 386
3.3. Zone Settling 387
3.4. Compression Settling 390
4. Sedimentation Tanks in Water Treatment 390
4.1. General Consideration 390
4.2. Inlet and Outlet Control 391
4.3. Tank Geometry 392
4.4. Short Circuiting 392
4.5. Detention Time 392
4.6. Tank Design 393
5. Sedimentation Tanks in Wastewater Treatment 394

5.1. General Consideration and Basis of Design 394
5.2. Regulatory Standards 395
5.3. Tank Types 395
6. Grit Chamber 398
6.1. General 398
6.2. Types of Grit Chambers 399
6.3. Velocity Control Devices 400
6.4. Design of Grit Chamber 402
7. Gravity Thickening in Sludge Treatment 403
7.1. Design of Sludge Thickeners 405
8. Recent Developments 406
8.1. Theory of Shallow Depth Settling 407
8.2. Tube Settlers 409
8.3. Lamella Separator 410
8.4. Other Improvements 411
9. Sedimentation in Air Streams 412
9.1. General 412
9.2. Gravity Settlers 413
10. Costs 414
10.1. General 414
10.2. Sedimentation Tanks 414
10.3. Gravity Thickeners 416
10.4. Tube Settlers 416
11. Design Examples 418
Nomenclature 426
References 427
Appendix: US Yearly Average Cost Index for Utilities 429
12 Dissolved Air Flotation
Lawrence K. Wang, Edward M. Fahey, and Zucheng Wu 431
1. Introduction 431

1.1. Adsorptive Bubble Separation Processes 431
1.2. Content and Objectives 434
2. Historical Development of Clarification Processes 435
2.1. Conventional Sedimentation Clarifiers 435
2.2. Innovative Flotation Clarifiers 437
3. Dissolved Air Flotation Process 440
3.1. Process Description 440
Contents xv
3.2. Process Configurations 441
3.3. Factors Affecting Dissolved Air Flotation 443
4. Dissolved Air Flotation Theory 444
4.1. Gas-to-Solids Ratio of Full Flow Pressurization System 444
4.2. Gas-to-Solids Ratio of Partial Flow Pressurization System 446
4.3. Gas-to-Solids Ratio of Recycle Flow Pressurization 447
4.4. Air Solubility in Water at 1 Atm 448
4.5. Pressure Calculations 449
4.6. Hydraulic Loading Rate 449
4.7. Solids Loading Rate 451
5. Design, Operation, and Performance 453
5.1. Operational Parameters 455
5.2. Performance and Reliability 455
6. Chemical Treatment 455
7. Sampling, Tests, and Monitoring 457
7.1. Sampling 457
7.2. Laboratory and Field Tests 457
8. Procedures and Apparatus for Chemical Coagulation Experiments 457
9. Procedures and Apparatus for Laboratory Dissolved Air Flotation Experiments 459
9.1. Full Flow Pressurization System 459
9.2. Partial Flow Pressurization System 460
9.3. Recycle Flow Pressurization System 461

10. Normal Operating Procedures 462
10.1. Physical Control 462
10.2. Startup 463
10.3. Routine Operations 464
10.4. Shutdown 464
11. Emergency Operating Procedures 464
11.1. Loss of Power 464
11.2. Loss of Other Treatment Units 465
12. Operation and Maintenance 465
12.1. Troubleshooting 465
12.2. Labor Requirements 465
12.3. Construction and O&M Costs 465
12.4. Energy Consumption 465
12.5. Maintenance Considerations 466
12.6. Environmental Impact and Safety Considerations 468
13. Recent Developments in Dissolved Air Flotation Technology 468
13.1. General Recent Developments 468
13.2. Physicochemical SBR-DAF Process for Industrial and Municipal Applications 470
13.3. Adsorption Flotation Processes 471
13.4. Dissolved Gas Flotation 471
13.5. Combined Sedimentation and Flotation 472
14. Application and Design Examples 472
Nomenclature 491
Acknowledgments 492
References 493
13 Gravity Filtration
J. Paul Chen, Shoou-Yuh Chang, Jerry Y. C. Huang,
E. Robert Baumann, and Yung-Tse Hung 501
1. Introduction 501
2. Physical Nature of Gravity Filtration 502

2.1. Transport Mechanism 502
2.2. Attachment Mechanisms 504
2.3. Detachment Mechanisms 504
3. Mathematical Models 504
3.1. Idealized Models 505
3.2. Empirical Models 509
xvi Contents
4. Design Considerations of Gravity Filters 510
4.1. Water Variables 510
4.2. Filter Physical Variables 511
4.3. Filter Operating Variables 517
5. Applications 522
5.1. Potable Water Filtration 522
5.2. Reclamation of Wasterwater 522
6. Design Examples 527
Nomenclature 539
References 540
14 Polymeric Adsorption and Regenerant Distillation
Lawrence K. Wang, Chein-Chi Chang, and Nazih K. Shammas 545
1. Introduction 545
2. Polymeric Adsorption Process Description 547
2.1. Process System 547
2.2. Process Steps 547
2.3. Regeneration Issues 547
3. Polymeric Adsorption Applications and Evaluation 548
3.1. Applications 548
3.2. Process Evaluation 550
4. Polymeric Adsorbents 550
4.1. Chemical Structure 550
4.2. Physical Properties 552

4.3. Adsorption Properties 552
5. Design Considerations 552
5.1. Adsorption Bed, Adsorbents, and Regenerants 552
5.2. Generated Residuals 555
6. Distillation 557
6.1. Distillation Process Description 557
6.2. Distillation Types and Modifications 557
6.3. Distillation Process Evaluation 560
7. Design and Application Examples 560
Acknowledgments 570
References 571
15 Granular Activated Carbon Adsorption
Yung-Tse Hung, Howard H. Lo, Lawrence K. Wang,
Jerry R. Taricska, and Kathleen Hung Li 573
1. Introduction 573
2. Process Flow Diagrams for GAC Process 576
3. Adsorption Column Models 577
4. Design of Granular Activated Carbon Columns 585
4.1. Design of GAC Columns 585
4.2. Pilot Plant and Laboratory Column Tests 590
5. Regeneration 591
6. Factors Affecting GAC Adsorption 592
6.1. Adsorbent Characteristics 592
6.2. Adsorbate Characteristics 592
7. Performance and Case Studies 593
8. Economics of Granular Activated Carbon System 595
9. Design Examples 602
10. Historical and Recent Developments in Granular Activated Carbon Adsorption 623
10.1. Adsorption Technology Milestones 623
10.2. Downflow Conventional Biological GAC Systems 625

10.3. Upflow Fluidized Bed Biological GAC System 627
Nomenclature 628
References 630
Contents xvii
16 Physicochemical Treatment Processes for Water Reuse
Saravanamuthu Vigneswaran, Huu Hao Ngo,
Durgananda Singh Chaudhary, and Yung-Tse Hung 635
1. Introduction 635
2. Conventional Physicochemical Treatment Processes 636
2.1. Principle 636
2.2. Application of the Physicochemical Processes in Wastewater Treatment and Reuse 651
3. Membrane Processes 658
3.1. Principle 658
3.2. Application of Membrane Processes 661
References 675
17 Introduction to Sludge Treatment
Duu-Jong Lee, Joo-Hwa Tay, Yung-Tse Hung, and Pin Jing He 677
1. The Origin of Sludge 677
2. Conditioning Processes 678
2.1. Coagulation 678
2.2. Flocculation 681
2.3. Conditioner Choice 681
2.4. Optimal Dose 682
3. Dewatering Processes 684
3.1. Dewatering Processes 684
3.2. Sludge Thickening 685
3.3. Sludge Dewatering 687
4. Stabilization Processes 691
4.1. Hydrolysis Processes 691
4.2. Digestion Processes 695

5. Thermal Processes 699
5.1. Sludge Incineration 699
5.2. Sludge Drying 701
5.3. Other Thermal Processes 702
References 703
Index 705
xviii Contents
Contributors
E. ROBERT BAUMANN, PhD • Department of Civil Engineering, Iowa State University of
Science and Technology, Ames, IA
CHEIN-CHI CHANG, PhD, PE • District of Columbia Water and Sewer Authority,
Washington, DC
S
HOOU-YUH CHANG, PhD, PE • Department of Civil and Environmental Engineering,
North Carolina A&T State University, Greensboro, NC
D
URGANANDA SINGH CHAUDHARY, PhD • Faculty of Engineering, University of Technology
Sydney (UTS), New South Wales, Australia
J. PAUL CHEN, PhD • Department of Chemical and Biomolecular Engineering, National
University of Singapore, Singapore
FRANK DELUISE, ME, PE • Emeritus Professor, Department of Mechanical Engineering,
University of Rhode Island, Kingston, RI
EDWARD M. FAHEY, ME • DAF Environmental, LLC, Hinsdale, MA
JOSEPH R. V. FLORA, PhD • Department of Civil & Environmental Engineering, University
of South Carolina, Columbia, SC
RAMESH K. GOEL, PhD • Department of Civil and Environmental Engineering, University
of Wisconsin, Madison, WI
PIN JING HE, PhD • School of Environmental Science and Engineering, Tongji University,
Shanghai, China
FREDERICK B. HIGGINS, PhD • Civil and Environmental Engineering Department, Temple

University, Philadelphia, PA
YUNG-TSE HUNG, PhD, PE, DEE • Department of Civil and Environmental Engineering,
Cleveland State University, Cleveland, OH
JERRY Y. C. HUANG, PhD • Department of Civil Engineering, University of Wisconsin–
Milwaukee, Milwaukee, WI
INDER JIT KUMAR, PhD • Eustance & Horowitz, P.C., Consulting Engineers, Circleville, NY
DUU-JONG LEE, PhD • Department of Chemical Engineering, National Taiwan University,
Taipei, Taiwan
KATHLEEN HUNG LI, MS • NEC Business Network Solutions, Irving, TX
YAN LI, PE, MS • Department of Environmental Management, State of Rhode Island,
Providence, RI
HOWARD LO, PhD • Department of Biological, Geological and Environmental Sciences,
Cleveland State University, Cleveland, OH
HUU HAO NGO, PhD • Faculty of Engineering, University of Technology Sydney (UTS),
New South Wales, Australia
NAZIH K. SHAMMAS, PhD • Graduate Environmental Engineering Program, Lenox Institute
of Water Technology, Lenox, MA
J
ERRY R. TARICSKA, PhD, PE • Hole Montes Inc., Naples, FL
xix
JOO-HWA TAY, PhD, PE • Division of Environmental and Water Resource Engineering,
Nanyang Technological University, Singapore
DAVID A. VACCARI, PhD, PE, DEE • Department of Civil, Environmental and Ocean Engineering,
Stevens Institute of Technology, Hoboken, NJ
S
ARAVANAMUTHU VIGNESWARAN, PhD, DSc, CPEng • Faculty of Engineering, University of
Technology Sydney (UTS), New South Wales, Australia
L
AWRENCE K. WANG, PhD, PE, DEE • Zorex Corporation, Newtonville, NY; Lenox Institute
of Water Technology, Lenox, MA; and Krofta Engineering Corporation, Lenox, MA

JY S. WU, PhD • Department of Civil Engineering, University of North Carolina at Char-
lotte, Charlotte, NC
Z
UCHENG WU, PhD • Department of Environmental Science and Engineering, Zhejiang
University, Hangzhou, People’s Republic of China
J
OHN Y. YANG, PhD • Niagara Technology Inc., Williamsville, NY
PAO-CHIANG YUAN, PhD • Technology Department, Jackson State University, Jackson, MS
xx Contributors
1
Screening and Comminution
Frank Deluise, Lawrence K. Wang, Shoou-Yuh Chang,
and Yung-Tse Hung
CONTENTS
FUNCTION OF SCREENS AND COMMINUTORS
TYPES OF SCREENS
PHYSICAL CHARACTERISTICS AND HYDRAULIC CONSIDERATIONS OF SCREENS
CLEANING METHODS FOR SCREENS
QUANTITY AND DISPOSAL OF SCREENINGS
COMMINUTORS
ENGINEERING SPECIFICATIONS AND EXPERIENCE
ENGINEERING DESIGN
DESIGN EXAMPLES
NOMENCLATURE
REFERENCES
1. FUNCTION OF SCREENS AND COMMINUTORS
In order for water and wastewater treatment plants to operate effectively, it is neces-
sary to remove or reduce early in the treatment process large suspended solid material
that might interfere with operations or damage equipment. Removal of solids may be
accomplished through the use of various size screens placed in the flow channel. Any

material removed may then be ground to a smaller size and returned to the process
stream or disposed of in an appropriate manner such as burying or incineration. An
alternative to actual removal of the solids by screening is to reduce the size of the solids
by grinding them while still in the waste stream; this grinding process is called com-
minution (1–8). Coarse screens (bar racks) and comminutors are usually located at the
very beginning of a treatment process, immediately preceding the grit chambers (Fig. 1).
To ensure continuous operation in a flow process, it is desirable to have the screens or
comminutors installed in parallel in the event of a breakdown or to provide for overhaul
of a unit. With this arrangement, flow is primarily through the comminutor and diverted
to the coarse (bar) screens only when necessary to shut down the comminutor. Fine
screens are usually placed after the coarse (bar) screens.
1
From: Handbook of Environmental Engineering, Volume 3: Physicochemical Treatment Processes
Edited by: L. K. Wang, Y T. Hung, and N. K. Shammas © The Humana Press Inc., Totowa, NJ
2 Frank Deluise et al.
2. TYPES OF SCREENS
2.1. Coarse Screens
Screens may be classified as coarse or fine. Coarse screens are usually called bar
screens or racks and are used where the wastewater contains large quantities of coarse
solids that might disrupt plant operations. These bar screens consist of parallel bars
spaced anywhere from 1.27 cm (1/2 in.) to 10.16 cm (4 in.) apart with no cross-members
other than those required for support. The size of the spacing depends on the type of
waste being treated (size and quantity of solids) and the type of equipment being pro-
tected downstream in the plant. These screens are placed either vertically or at an
angle in the flow channel. Installing screens at an angle allows easier cleaning (par-
ticularly if by hand) and more screen area per channel depth, but obviously requires
more space.
2.2. Fine Screens
Fine screens have openings of less than 0.25 in. and are used to remove solids
smaller than those retained on bar racks. They are used primarily in water or wastewater

containing little or no coarse solids. In many instances, fine screens are used for the recov-
ery of valuable materials that exist as finely divided solids in industrial waste streams.
Most fine screens use a relatively fine mesh screen cloth (openings anywhere from
0.005 to 0.126 in.) rather than bars to intercept the solids. A screen cloth covers discs or
drums, which rotate through the wastewater. The disc-type screen (Fig. 2) is a vertical
hoop with a screen cloth covering the area within the hoop, and mounted on a horizon-
tal shaft that is positioned slightly above the surface of the water. Water flows through
the screen parallel to the horizontal shaft and the solids are retained on the screen, which
carries them out of the water as it rotates. Solids may then be removed from the upper
part of the screen by water sprays or mechanical brushing.
The drum-type screen (Fig. 3) consists of a cylinder covered by a screen cloth with
the drum rotating on a horizontal axis, slightly less than half submerged. Wastewater
enters the inside of the drum at one end and flows outward through the screen cloth.
Solids collect inside the drum on the screen cloth and are carried out of the water as the
drum rotates. Once out of the water, the solids may be removed by backwater sprays,
forcing the solids off the screen into collecting troughs.
Fig. 1. Location of screens and comminutors in a wastewater treatment plant.
Screening and Comminution 3
3. PHYSICAL CHARACTERISTICS AND HYDRAULIC
CONSIDERATIONS OF SCREENS
The physical characteristics of bar racks and screens depend on the use for which
the unit is intended. Coarse bar racks, sometimes called trash racks, with 7.62 or
10.16 cm (3 or 4 in.) spacing are used to intercept unusually large solids and there-
fore must be of rugged construction to withstand possible large impacts. Bar screens
with smaller spacing may be of less rugged construction. As previously mentioned,
the spacing between bars depends on the size and quantity of solids being intercepted.
Although a screen’s primary purpose is to protect equipment in a sewage-treatment
plant, spacings smaller than 2.54 cm (1 in.) are usually not necessary because today’s
sewage sludge pumps can handle solids passing through the screen. Typical bar
screens are shown in Fig. 4.

Fig. 2. Revolving disc screen: (a) screen front (inlet side) view and (b) screen side view section.
Fig. 3. Revolving drum screen.
4 Frank Deluise et al.
The screen bars are usually rectangular in cross-section and their size depends on the
size (width and depth) of the screen channel as well as the conditions under which
the screen will be operating. The longer the unsupported length of the bar, the larger is
the required cross-section. Bars up to 1.83 m (6 ft) in length are usually no smaller than
0.635 × 5.08 cm (1/4 × 2 in.), while bars up to 3.66 m (12 ft) long might be
0.952 × 6.35 cm (3/8 × 2.5 in.). Longer bars or bars used for operating conditions caus-
ing unusual stress might be as large as 1.59 × 7.62 cm (5/8 × 3 in.). The bars must be
designed to withstand bending as well as impact stresses due to the accumulation of
solids on the screen.
Many screens, particularly those that are hand-cleaned, are installed with bars at an
angle between 60º and 90º with the horizontal. With the bars placed at an angle, the
screenings will tend to accumulate near the top of the screen. In addition, the velocity
through the screen will be low enough to prevent objects from being forced through the
screen. Optimum horizontal velocity through the bars is approx 0.610 m/s (2 ft/s). If
velocities get too low, sedimentation will take place in the screen channel. In the design
of the screen channel, it is desirable to have the flow evenly distributed across the
screen by having several feet of straight channel preceding the screen. Flow entering at
an angle to the screen would tend to create uneven distribution of solids across the
screen and prevent the proper operation of the equipment.
The required size of the screen channel depends on the volume flow rate and the free
space available between the bars. If a net area ratio is defined as the free area between
bars divided by the total area occupied by the screen, then a table such as Table 1 may
be set up showing the net area ratio for various combinations of bar size openings.
The bar spacing should be kept as large as practical and the bar thickness as small as
practical in order to obtain the highest net area ratio possible. Once the volume flow
rates are known and the net area ratio is determined, the screen channel size may be
determined. The maximum volume flow rate in cubic meters per second divided by the

optimum velocity of 0.610 m/s will yield the net area required. This net area divided by
Fig. 4. Elements of a mechanical bar screen and grit collector.
Screening and Comminution 5
the net area ratio selected will give the total wet area required for the channel. With this
known area, the width and depth of the channel may be determined. Usually the maxi-
mum width or depth of the channel is limited by considerations other than the actual
screening process. Too wide a screen could present problems in cleaning, and therefore
the maximum practical width for a channel is about 4.27 m (14 ft); the minimum width is
about 0.610 m (2 ft). The depth of liquid in the channel is usually kept as shallow as
possible so that the head loss through the plant will be a minimum. The wet area divided
by the known limiting width or depth will thus provide the dimensions of the channel.
From Bernoulli’s equation, the theoretical head loss for frictionless, adiabatic flow
through the bar screen is
(1)
where h = head loss, m (ft), V
2
= velocity through bar screen, m/s (ft/s), V
1
= velocity
ahead of bar screen, m/s (ft/s), and g = 9.806 m/s
2
(32.17 ft/s
2
).
To determine the actual head loss, the above expression may be modified by a dis-
charge coefficient, C
D
, to account for deviation from theoretical conditions. Values of C
D
should be determined experimentally, but a typical average value is 0.7. The equation

then becomes
(2)
(2a)
(2b)
4. CLEANING METHODS FOR SCREENS
Bar screens or racks may be cleaned by hand or by machine. Hand-cleaning limits
the length of screen that may be used to that which may be conveniently raked by hand.
The cleaning is accomplished using a specially designed rake with teeth that fit between
the bars of the rack. The rake is pulled up toward the top of the screen carrying the
hVV=−
(
)
0 0222
2
2
1
2
. with English units
hVV=−
(
)
0 0728
2
2
1
2
. with SI units
h
VV
Cg

D
=
−
2
2
1
2
2
h
VV
g
=
−
2
2
1
2
2
Table 1
Net Area Ratios for Bar Size and Openings
Bar size Opening
cm in. cm in. Net area ratio
0.635
1
⁄
4 1.27
1
⁄
2 0.667
0.635

1
⁄
4 2.54 1 0.800
0.635
1
⁄
4 3.81 1
1
⁄
2 0.856
0.952
3
⁄
8 1.27
1
⁄
2 0.572
0.952
3
⁄
8 2.54 1 0.728
0.952
3
⁄
8 3.81 1
1
⁄
2 0.800
1.270
1

⁄
2 1.27
1
⁄
2 0.500
1.270
1
⁄
2 2.54 1 0.667
1.270
1
⁄
2 3.81 1
1
⁄
2 0.750
screenings with it. At the top of the screen, the screenings are deposited on a grid or
perforated plate for drainage and then removed for shredding and return to the channel
or for incineration or burial. Hand-cleaning requires a great deal of manual labor and is
an unpleasant job. Because hand-cleaning is not continuous, plant operations may be
materially affected by undue plugging of the screens before cleaning as well as by large
surges of flow when the screens are finally cleaned. Plugging of the screens could cause
troublesome deposits in the lines leading to the bar screens, and surges after cleaning
could disrupt the normally smooth operations of units following the screens.
Mechanical cleaning overcomes many of the problems associated with hand-cleaning.
Although the initial cost of a mechanically cleaned screen will be much greater than for a
hand-cleaned screen, the improvement in plant efficiency, particularly in large installa-
tions, usually justifies the higher cost. The ability to operate the cleaning mechanism on
an automatically controlled schedule avoids the flooding and surging through the plant
associated with plugging and unplugging of the screens. After a short while, a preset auto-

matic cleaning cycle may be easily established to keep the bars relatively clear at all times.
Mechanically cleaned screens use moving rakes attached to either chains or cables to
carry the screenings to the top of the screen. At the top of the screen, rake wiper blades
sweep the screenings into containers or onto conveyor belts for disposal. The teeth on
the rakes project between the screen bars either from the front or the back of the rack.
Both methods have their advantages and disadvantages. The front-cleaned models have
the rakes passing down through the wastewater in front of the rack and then up the face
of the rack. This method provides excellent cleaning efficiency, but the rakes may
potentially become jammed as they pass through any accumulation of solids at the base
of the screen on the downward travel. A modification of the front-cleaned model has the
rakes traveling down behind the screen and through a boot under the screen, and then
moving up the front of the screen. The back-cleaned models eliminate the jamming
problem by having the rakes travel down through the water behind the screen and then
travel up behind the screen with teeth projecting through the bars far enough to pick up
solids deposited on the front of the screen. In models where the rake travels up the back
of the screen, the bars are fixed only at the bottom of the screen because the rake must
project all the way through the bars. It is thus possible for the bars to move as they are
supported only by the traveling rake teeth. With movement of the bars, it is possible for
solids substantially larger than those designed for to pass through the screen. Another
drawback of the back-cleaned screen is that any solids not removed from the rakes
because of faulty wiper blades are returned to the flow behind the screen. Several man-
ufacturers have modified both the front- and back-cleaned screens to help reduce some
of these problems.
5. QUANTITY AND DISPOSAL OF SCREENINGS
The quantity of screenings is obviously greatly affected by the type and size of screen
openings and the nature of the waste stream being screened. The curves in Fig. 5 show
the average and maximum quantities of screenings in cubic feet per 10
6
gallons
(ft

3
/MG) that might be obtained from sewage for different sized openings between
bars. Data for these curves were obtained from 133 installations of hand-cleaned and
mechanically cleaned bar screens in the United States. It can be seen that the average
6 Frank Deluise et al.